1. Field of the Invention
This invention relates to diamonds made by the chemical vapor deposition of monolithic diamond onto a substrate, and more particularly to method and apparatus for the separation of diamond from the substrate.
Various methods are known for the synthetic production and shaping of diamond. For example, U.S. Pat. No. 3,895,313 discloses first forming a synthetic diamond sphere and machining away a large fraction of the sphere to form a diamond window. Diamond windows are used for lasers. Due to prior art size limitations, a large number of small windows are required for large lasers. In particular, the deposition of diamond coatings on substrates to produce cutting and abrasive tools is known.
One class of methods developed in recent years for synthetic diamond deposition consists of the chemical vapor deposition (hereinafter sometimes "CVD") methods. For a general summary of various diamond deposition methods including CVD methods, reference is made to Chemical & Engineering news, 67(20), 24-39 (May 15, 1989), incorporated herein by reference. Reference in the article to a free standing sheet of diamond is probably the result of one of the present inventors showing one of the authors a diamond sheet about one inch square made during the experimental development of the present invention. No disclosure was made as to the technique used to make the sheet of diamond.
In the CVD methods, a mixture of hydrogen and a hydrocarbon gas such as methane is thermally activated and passed into contact with a substrate. The hydrogen gas is converted to atomic hydrogen which reacts with the hydrocarbon to form elemental carbon, which deposits on the substrate in the form of diamond. Many of the CVD diamond coating methods, hereinafter referred to as "filament" methods, employ one or more resistance heating units including heated wires or filaments, typically at temperatures of at least 2000.degree. C., to provide the high activation temperatures at which these conversions take place.
Relatively thick diamond coatings are required in the manufacture of such articles as cutting tools. However, a problem which often arises is the failure of thick diamond coatings to adhere to the substrate, as a result or differences in coefficient of thermal expansion between the diamond and the substrate.
2. Description of the Prior Art
Thus, for example, cutting tools comprising a diamond layer on substrates other than the molybdenum used in the original deposition are often desired. The coefficients of thermal expansion of diamond and molybdenum are so different that stresses are produced in the diamond coated molybdenum as it cools from the temperature at which diamond deposition takes place. Thin diamond coatings are usually elastic enough to withstand such stresses, but thick coatings of the type desired on cutting tools may cause separation of diamond from the molybdenum substrate and/or catastrophic failure of the diamond layer in the form of severe cracking and fragmentation.